Smylie was successful as a tennis player in the 1980s and at the beginning of the 1990s, especially in doubles. She won a total of 36 women's doubles titles. Together with Kathy Jordan , she won the Wimbledon Grand Slam tournament in 1985 . In addition, she was four times in the double-finals of a Grand Slam tournament. At the 1988 Olympic Games in Seoul , she won the bronze medal together with her partner Wendy Turnbull . In March 1988 she was number 5 in the world in women's doubles.
In mixed she won the US Open in 1983 and 1990 and the 1991 Wimbledon tournament.
Smylie also won two individual titles in her career, namely at the WTA tournaments in Kansas City (1983) and in Oklahoma City (1987).